Relative ease or difficulty of steering has in the past been largely a matter of psychology, of comparison rather than of measurement. One driver may find a car difficult to steer that another finds easy. Safety is the first essential, then comfort. Because the parts used in steering seldom break, present practice is considered safe, but the steering-ratio is very important. A low ratio that produces fast steering-effects may be entirely safe in the hands of a strong, safe, experienced driver, but absolutely unsafe in those of a weaker driver, even though he may be expert. Fatigue, however, will eventually affect the strong as well as the weak driver, so that comfort enters as well as safety.
With a view to eliminating the personal factor and determining by exact measurement the steering-effort exerted by a driver and the reactions termed road shock, road fight, shimmying and the like, instruments have been devised to produce a graphical record simultaneously of (a) the amount, of steering-effort and the reactions at the steering-wheel, and (b) the stress imposed upon the drag-link; note is also made whether the steering-effort is to the right or to the left.
The details of construction and operation of these instruments are described and the results of tests made on roads of various types when the car is traveling at various rates of speed are discussed. A study also was made of the comparative effort exerted in making turns to the right and to the left, in suddenly reversing the direction of stress, and of the effect produced by the impact of a wheel's striking the curbstone.
Statements are made that tests show that the drag-link stress of a car not in motion ranges from 400 to 600 lb., that balloon tires require 50 per cent greater steering-effort than do high-pressure tires, that in some high-grade popular cars a difference of only a few ounces of steering-effort changes unsatisfactory conditions into very satisfactory results, that differences as great as 450 per cent have been found in the friction of the steering-knuckle thrust-bearings of current models of well-known cars, and that a difference is apparent between the steering-efforts required in cars having and in those not having center-point steering.